The introduction of statins (e.g., Mevacor®, Lipitor®, etc.) has reduced mortality from heart attack and stroke by about one-third. However, heart attack and stroke remain the major cause of death and disability, particularly in the United States and in Western European countries. Heart attack and stroke are the result of a chronic inflammatory condition, which is called atherosclerosis.
Several causative factors are implicated in the development of cardiovascular disease including hereditary predisposition to the disease, gender, lifestyle factors such as smoking and diet, age, hypertension, and hyperlipidemia, including hypercholesterolemia. Several of these factors, particularly hyperlipidemia and hypercholesteremia (high blood cholesterol concentrations) provide a significant risk factor associated with atherosclerosis.
Cholesterol is present in the blood as free and esterified cholesterol within lipoprotein particles, commonly known as chylomicrons, very low density lipoproteins (VLDLs), low density lipoproteins (LDLs), and high density lipoproteins (HDLs). Concentration of total cholesterol in the blood is influenced by (1) absorption of cholesterol from the digestive tract, (2) synthesis of cholesterol from dietary constituents such as carbohydrates, proteins, fats and ethanol, and (3) removal of cholesterol from blood by tissues, especially the liver, and subsequent conversion of the cholesterol to bile acids, steroid hormones, and biliary cholesterol.
Maintenance of blood cholesterol concentrations is influenced by both genetic and environmental factors. Genetic factors include concentration of rate-limiting enzymes in cholesterol biosynthesis, concentration of receptors for low density lipoproteins in the liver, concentration of rate-limiting enzymes for conversion of cholesterols bile acids, rates of synthesis and secretion of lipoproteins and gender of person. Environmental factors influencing the hemostasis of blood cholesterol concentration in humans include dietary composition, incidence of smoking, physical activity, and use of a variety of pharmaceutical agents. Dietary variables include the amount and type of fat (saturated and polyunsaturated fatty acids), the amount of cholesterol, amount and type of fiber, and perhaps the amounts of vitamins such as vitamin C and D and minerals such as calcium.
Low density lipoprotein (LDL) oxidation has been strongly implicated in the pathogenesis of atherosclerosis. High density lipoprotein (HDL) has been found to be capable of protecting against LDL oxidation, but in some instances has been found to accelerate LDL oxidation. Important initiating factors in atherosclerosis include the production of LDL-derived oxidized phospholipids.
Normal HDL has the capacity to prevent the formation of these oxidized phospholipids and also to inactivate these oxidized phospholipids once they have formed. However, under some circumstances HDL can be converted from an anti-inflammatory molecule to a pro-inflammatory molecule that actually promotes the formation of these oxidized phospholipids.
It has been suggested that HDL and LDL function as part of the innate immune system (Navab et al. (2001) Arterioscler. Thromb. Vasc. Biol., 21: 481-488). The generation of anti-inflammatory HDL has been achieved using class A amphipathic helical peptides that mimic the major protein of HDL, apolipoprotein A-I (apo A-I) (see, e.g., WO 02/15923).
Age-related macular degeneration (AMD) is the most frequent cause of legal blindness in the elderly in industrial countries (Van Leeuwen et al. (2003) European Journal of Epidemiology 18: 845-854). It is a heterogeneous disease, which is characterized by progressive loss of central, high acuity vision. For the patient it compromises dramatically quality of life, since they lose their ability to read, to recognize faces and day-to-day tasks become major obstacles. According to the WHO a total of 30-50 million individuals are affected and about 14 million people are blind or severely visually impaired due to AMD (Gehrs et al., (2006) Annals of Medicine 38:450-471).
The most prominent clinical and histopathological lesions of AMD involve the choriocapillaris, Bruch's membrane, and the retinal pigment epithelium (RPE) (Ambati et al. (2003) Survey of Opthalmology 48:257-293). The choriocapillaris is a highly specialized capillary plexus with the highest blood flow rate in the body which interacts with the highly metabolic active RPE. The RPE forms the outer blood-retina barrier and supplies the photoreceptors, the sensory cells in the eye, with nutriments as well as phagocytes daily shed outer photoreceptor segments which are degraded and partially recycled. Under normal conditions unrecycled end products are rendered into the choriocapillaris. Bruch's membrane is a five layer connective tissue between the RPE and choriocapillaris resembling an arterial intima in its function (Curcio et al. (2001) Invest Opthalmol Vis Sci 42:265-274). With age Bruch's membrane undergoes distinctive degenerative changes. One major characteristic feature next to thickening is the accumulation of neutral lipids, which build up a diffusion barrier between the RPE and choriocapillaris compromising RPE and photoreceptor function (Curcio et al. (2001) Invest Opthalmol Vis Sci 42:265-274; Pauleikhoff et al. (1990) Opthalmology 97:171-178; Moore et al. (1995) Invest Opthalmol Vis Sci 36:1290-1297).
In early stages of AMD an additional deposition of debris is observed between the basal membrane of the RPE (1st layer of Bruch's membrane) and the inner collagenous layer (2nd layer of Bruch's membrane). This debris is called basal linear deposits and drusen, both rich in lipids and hallmarks of AMD, impairing even more the diffusion along Bruch's membrane (Gehrs et al, (2006) Annals of Medicine 38:450-471; Curcio et al. (1999) Arch Opthalmol 117:329-339; Curcio et al. (2005) Experimental Eye Research 81: 731-741; Haimovici et al. (2001) Invest Opthalmol Vis Sci 42:1592-1599). Furthermore, cytotoxic and lipid rich, metabolic end products, called lipofuscin, accumulate in the RPE cells (Beatty et al. (2000) Surv Opthalmol 45:115-134). All these conditions together cause oxidative stress and inflammation resulting in RPE atrophy and successively photoreceptor degeneration (Kopitz et al. (2004) Biochimie 86: 825-831). This atrophy of RPE and photoreceptors is called the dry form of AMD and progresses slowly and irreversibly. Currently a treatment or prevention of this form of AMD, which affect about 85-90% of all AMD patients, does not exist (Van Leeuwen et al. (2003) European Journal of Epidemiology 18: 845-854).
The second form of AMD is called wet AMD and can arise from the dry form. It affects about 10-15% of all AMD patients and is marked by the growth of a pathological vessel from the choriocapillaris into the subretinal space, called choroidal neovascularization (CNV) (Gehrs et al. (2006) Annals of Medicine 38:450-471 and Ambati et al. (2003) Survey of Opthalmology 48:257-293). It causes a rapid, irreversible vision loss due to leakage, bleeding, and scaring (Ambati et al. (2003) Survey of Opthalmology 48:257-293). In the last 5 years antiangiogentic therapies were developed targeting vascular endothelial growth factor, which could show success in slowing down the progression of vision loss (Michels et al. (2006) Expert Opin Investig Drugs 15:779-793).
In general, current therapies use antibodies or antibody fragments against VEGF, which are injected into the vitreous body of the eye (Michels et al. (2006)). A prevention therapy of wet AMD does not exist (Gehrs et al. (2006)), which would be especially desirable when the vision in one eye is already largely compromised and the second eye shows definite risk factors for a progression like e.g. large soft drusen (Ambati et al. (2003)).
Lipids are hydrophobic and cannot simply dissolve in an aqueous medium such as blood. In order to be transported in blood lipids have to be assembled in particles called lipoproteins. Specialized proteins called apolipoproteins help to form and stabilize these particles. There are several classes of apolipoproteins (A-JM, a). Basically their functional structures are comparable which are amphipathic helices.
Apolipoprotein mimetic peptides are synthetic helical lipid accepting peptides mimicking the function of an apolipoprotein (Mendez et al. (1994) J. Clin. Invest 94:1698-1705). One of the best known is the ApoA-I mimetic peptide 4F, has been shown to treat atherosclerosis (Anantharamaiah et al. (2006) Current Opinion in Lipidology 17:233-237). It is available as L-4F and as its stereoisomer D-4F. It consists of 18 amino acids, is well water-soluble, a high potent lipid acceptor, and acts as a highly anti-inflammatory (Navab et al. (2006) Nat. Clin. Pract. Cardiovasc. Med. 3:540-547). D-4F is based on D-amino acids and is compared to L-4F more resistant to degradation and can be taken orally (Anantharamaiah et al. (2006)). A phase I clinical trial with D-4F already started. So far no side effects of D-4F are described.